MAJOR SPOILERS FOR THE WHOLE MOVIE
Beginning (approximate order):
The world at the beginning is a Homura surveillance state with magical quadcopter drones and magical cameras everywhere, and homura seems to hijacked the magical girl process cause when girls receive the calling (a ringing phone literally appears in front of them) homura is the one that answers
Mami, Kyoko, and Sayaka (and maybe Nagisa) do magical girl activities and have an uneasy truce/alliance with Homura who is their grief cubes (?) dealer and seems to know more than she lets on, the three of them keep thinking they need to invite Madoka to their activities before getting confused because Madoka is just a regular non-magical girl transfer student they are friends with... These two things especially bother Sayaka
The new characters (I forgot their names so I'll just refer to their hair colours) Purple, Green, and Orange appear in school one day and everybody acts like they were always students which unnerves Homura, especially when Purple singles out Madoka as "Margarita" and gets uncomfortably close (while Green gets friendly with Kyoko and Orange with Nagisa & Mami)
Madoka returns to an empty home one day and there are phones literally everywhere, all of them suddenly start ringing for her and Purple is there trying to get her to awaken (?) until Homura appears and they have a fight. Devil homura appears to have the upper hand until magical girl Green and Orange appear too on Purple's side, and Homura loses a wing, and then Madoka snaps back to sitting with her family and hangs up the phone as if everything was a daydream
The plot splits into two at this point, Sayaka goes to confront Homura:
Homura gives vague hints and ominous warnings, but Sayaka insists so they walk through a lot of trippy imagery until they reach a library (apparently called Nazukasokotsune?), Kyubey is also there along with Purple girl
Homura finds out Purple is Walpurgis (and that's why she looks like her?) and fights some witches without her devil form which doesn't work here, while Sayaka is shocked to find out she becomes a witch somehow
Homura and Sayaka eventually escape, also Sakaya is no longer bandaged anymore
Meanwhile the rest of the girls are having sweets party with Green and Orange:
At one point cupcakes triggers Green's trauma (that caused her to become a witch?) and she runs off angry that everyone is so happy, and Madoka follows behind to apologize
Green reveals she is a magical girl and a witch (who was originally saved and is now in despair again?), and attempts to capture a confused Madoka until Kyoko saves her and there is an underwater witch fight
Eventually Mami & reinforcements arrive and Green is pacified but Orange has captured Madoka
Climax of the story (ngl I start to lose the plot around here):
The girls reunite while everything goes to hell, orange goes full witch mode, walpurgis is come, and also Madoka's witch returns because of Homura's actions
Sayaka goes hikikomori mode briefly, but then Nagisa snaps her out of it with her carefree attitude not caring about gods/devils/etc, and then Sayaka saves the day
Flashback scene with a blond nun character "Margarita" in magical girl nunnery who made the proto-madoka wish to "save all magical girls", then became overwhelmed, fell to darkness becoming walpurgis, forever seeking her own "Margarita" to save her until God!Madoka
Eventually the girls work together and defeat all the witches (Mami ults, Nagisa defeats orange by means of giant magical kitchenaid, etc.), and Madoka comforts/saves Walpurgis
ENDING: Madoka gets gold eyes again and is called to God!Madoka and walks towards her, Homura despairs that Madoka's fate is to always either become a witch or a god until the other girls encourage her saying that she can do something about it as the "devil". There is a brief metaphysical god vs devil fight, scene of Homura lying on Madoka's lap on a bench and Madoka says they'll be together (?), Madoka who was walking towards God!Madoka mouths words we can't hear (gut impression was "sorry"), God!Madoka disappears, Homura is lying alone on the same bench but smiling happily.
Post-credits: Sequel hook, Kyubey is in Nazukasokotsune/library and is happy about the experiment